STriDER: Self-excited Tripedal Dynamic Experimental Robot

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Self-excited Tripedal Dynamic Experimental Robot
Principal Investigator Dr. Dennis Hong
Researchers Ping Ren
Joe Hays
Mechanical Details
DOF 12
Motors Robotis Dynamixel RX-28

STriDER (Self-excited Tripedal Dynamic Experimental Robot) is a novel three-legged walking machine that exploits the concept of actuated passive dynamic locomotion to dynamically walk with high energy efficiency and minimal control. Unlike other passive dynamic walking machines, this unique tripedal locomotion robot is inherently stable with its tripod stance and can change directions while walking.


Operational Concept

During a step, two legs act as stance legs while the other acts as a swing leg. The legs are oriented to push the center of gravity outside of the stance legs to initiate a step. As the body of the robot falls forward, the swing leg naturally swings in between the two stance legs and catches the fall. The body also rotates 180 degrees, preventing the legs from tangling up. Once all three legs are in contact with the ground, the robot regains its stability and the posture of the robot is then reset in preparation for the next step. Gaits for changing directions are implemented in a rather interesting way: by changing the sequence of choice of the swing leg, the tripedal gait can move the robot in 60° interval directions for each step.


The simple tripod configuration and tripedal gait of STriDER has many advantages over other legged robots; it has a simple kinematic structure; it is inherently stable (like a camera tripod); it is simple to control as the motion is a simple falling in a predetermined direction and catching its fall; it is energy efficient, exploiting the actuated passive dynamic locomotion concept utilizing its built in dynamics; it is lightweight enabling it to be launched to difficult to access areas; and it is tall making it ideal for deploying and positioning sensors at high position for surveillance, for example.

Goals and Objectives

In this research, we study the issues of actuated passive dynamic locomotion, optimizing physical design parameters for dynamically walking robots, and the design of this novel locomotion system by means of a combination of theoretical analysis, computer simulation, and designing and construction of prototypes for experimentation. The overall research objectives are:

  • Analyze and synthesize various gait strategies for changing directions and path planning
  • Study the three-dimensional kinematics and dynamics of STriDER
  • Improve understanding of the effects of design parameters on the quality of gaits and find optimal mechanical design parameters with dynamic considerations
  • Design and fabricate a working robot prototype to verify the analytical model and evaluate the concept.


Journal Papers

  1. Ren,P., Hong, D.W., and Morazzani, I., “Forward and Inverse Displacement Analysis of A Novel Three-Legged Mobile Robot Based on the Kinematics of In-parallel Manipulators,” ASME Journal of Mechanisms and Robotics, submitted

Book Chapters

  1. Morazzani, I., Lahr, D., Hong, D.W., Ren, P., “Novel Tripedal Mobile Robot and Considerations for Gait Planning Strategies Based on Kinematics,” Recent Progress in Robitics: Viable Robotic Service to Human, pp.35-48, Springer-Verlag Berlin Heidelberg, 2008

Conference Papers

  1. Ren, P., Hong, D.W., “Instantaneous Kinematics and Singularity Analysis of a Novel Three-Legged Mobile Robot with Active S-R-R-R Legs,” 32nd ASME Mechanisms and Robotics Conference, August 3-6, 2008, Brooklyn, New York, USA
  2. Ren, P.,Morazzani, I., and Hong, D.W., “Forward and Inverse Displacement Analysis of a Novel Three-legged Mobile Robot base on the Kinematics of In-parallel Manipulators,” 31st ASME Mechanisms and Robotics Conference , September 4-7, 2007, Las Vegas, Nevada, USA
  3. J.R. Heaston and D.W. Hong, "Design of a novel tripedal locomotion robot and simulation of a dynamic gait for a single step," ASME Mechanisms and Robotics Conference, September 2007.
  4. Hong, D. W., “Biologically Inspired Locomotion Strategies: Novel Ground Mobile Robots at RoMeLa”, The 3rd International Conference on Ubiquitous Robots and Ambient Intelligence, Seoul, S. Korea, October 15-17, 2006
  5. Heaston, J. R., Hong, D. W., Morazzani, I., Ren, P., Goldman, G., “STriDER: Self-Excited Tripedal Dynamic Experimental Robot”, 2007 IEEE International Conference on Robotics and Automation, Roma, Italy, April 10-14, 2007
  6. D.W. Hong and D.F Lahr. "Synthesis of the body swing rotator joint aligning mechanism for the abductor joint of a novel tripedal locomotion robot," ASME Mechanisms and Robotics Conference, September 2007.


  1. Best Paper Award, The 13th International Conference on Advanced Robotics, 2007
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